1. Field of the Invention
The present invention relates to an optical reception device and an optical switch network that are used in a communication network or an interconnected network of parallel computers.
2. Description of the Related Art
An optical switch that uses liquid crystal is described in Reference 1: Japanese Patent Laid-open No. 273603/1993. In this optical switch device, a first waveguide unit is provided on one surface of a liquid crystal panel having N rows and M columns and a second waveguide unit is provided on the other side. The first waveguide unit has N branching waveguides each having one input and M outputs, the branching waveguides being arranged such that the M output terminals of each branching waveguide are directed toward optical shutters in the column direction of the panel without overlap. In addition, the second waveguide unit has M condensing waveguides each having N inputs and one output, the condensing waveguides being arranged such that the N input terminals of each of these condensing waveguides are directed toward optical shutters in the row direction of the panel without overlap. This configuration can provide an optical switch device that, compared to the prior art, enables a greater reduction of crosstalk, facilitates packaging, and facilitates handling of wavelength division multiplexed optical signals.
An image display device that employs ON/OFF control of light by means of liquid crystal is described on page 52 of “Technology of Reflective Color Crystal Displays” (CMC BOOKS Co., Japan, 3-1999).
An optical switch network in which optical switches are used to switch optical signals is expected to serve as a means for realizing a high-capacity network that cannot be attained by a conventional electrical network. So far, optical switches that take advantage of the electro-optic effect or acousto-optic effect of crystals such as lithium niobate and optical switches that employ semiconductor optical amplifiers as gates have been designed, and various configurations have been proposed regarding optical switch networks that employ these components (for example, Reference 2: Japanese Patent Laid-open No. 197078/2000)
When an optical switch network is constituted using, for example, optical switches that employ the electro-optic effect and acousto-optic effect of crystals such as lithium niobate or optical switches that use semiconductor optical amplifiers as gates, the volume occupied by the optical switches alone becomes considerable as the number of switches in the optical switch network increases. For example, a 1000×1000 switch matrix by switches measuring one cm square would require a space measuring 10 m×10 m if the switches are arranged on a plane. Accordingly, the switch devices and the optical reception devices and optical switch network that include the switch devices, would result in an extremely bulky construction.
To overcome this problem, liquid crystal may be used to constitute the switch matrix. The use of liquid crystal enables a minimization of the area of switch units to several tens of μm, and, since the use of liquid crystal facilitates integration, a substantial reduction in the size of the switch matrix. The size of the optical reception devices and optical switch network can be reduced correspondingly.
The above example that indicates that liquid crystal can be used in an optical switch device accords with the prior art. Although the concept of using switches that are constituted by liquid crystal arranged in matrix form to switch optical paths is described in the optical switch device that is disclosed in Reference 1, nothing is disclosed regarding the actual construction that enables ON/OFF switching of the liquid crystal.
On the other hand, the element configuration that enables ON/OFF switching of liquid crystal in an image display device that uses liquid crystal is described on page 52 of the above-described “Technology of Reflective Color Liquid Crystal Displays” by CMC BOOKS Co. Still, no example exists that mentions the method of installing optical fiber in a liquid crystal optical shutter.
However, the portion in which an optical fiber is fitted to a liquid crystal shutter in an optical switch that uses liquid crystal is an important technical point that strongly influences overall performance. More specifically, the positional relation of each of the end portions of the pair of optical fibers on the input and output sides has a major bearing on performance.
First, it is important that the end surface (the contact surface of the end surface when the end surface is curved) of each optical fiber be mutually parallel. If the end surfaces are not parallel, the beam that is emitted from the optical fiber on the emitting side will not be directed precisely into the optical fiber on the input side, with the result that even though a beam is incident, the beam will not be precisely propagated in the input optical fiber, resulting in a large attenuation of light.
Second, it is important that the optical axes of the optical fibers be precisely aligned. If the optical axes are not aligned, the beam that is emitted from the optical fiber on the emitting side will not be directed precisely into the optical fiber on the input side.
Third, it is important that the two ends of the optical fibers be as close together as possible. The beam that is emitted from an optical fiber is diffused, and separation between the emitting end and input end therefore results in the input of only a portion of the emitted beam, resulting in significant attenuation.
When considering the installation of the input and output optical fibers in a liquid crystal display device of the prior art, solving the above-described first and second points has been problematic, but added to these two points, solving the third point has been insurmountable. This is because the substrate for encapsulating the liquid crystal in a normal liquid crystal display device is incorporated in the substrate for forming the liquid crystal driving circuits, and decreasing the gap between the two end portions is therefore difficult when the liquid crystal display device is installed between the input and output optical fibers.